Tait T855 - Page 191

M850-00 T856/857 Fault Finding C5.15
Copyright TEL 31/09/98
5.7.4 T856 Drive Amplifier
10.5V on Q315
collector?
Check continuity
of power rails
& DC paths to
Q365 & Q370.
Check signal
path to output
incl. output
socket (SK310).
Key exciter
& lock
synthesiser.
NN
YY
Y
Check VCO.
N
Y
Y
N
Y
Y
N
Y
N
Y
Check 9V &
13.8V supplies.
Check
regulators.
Check temp.
shutdown
circuit.
N
Y
N
Y
N
Y
10.5V on Q350
collector?
10.5V on Q355
collector?
13.8V on
IC350 pin 8?
11.5V on
IC350 pin 7?
N
Check lock det.
path back to
synth. IC740,
IC750, Q325.
Check TP305
>+8V.
Check TP320
<0.6V.
Check Q310,
Q315 circuitry
& IC350.
>2V RF at
VCO output?
>1V RF
at R381?
N Check attenuator
pad #R517, #R518,
#R519.
>0.5V RF at
Q350 base?
Check C355, C358,
C360, Q350, D340,
D380, D360, L320.
N
Check Q350.
>1V RF at
Q355 base?
Check signal
path between
Q350 & Q355.
>6V RF at
Q355 collector?
Check Q355.
>5V RF at
C362, #R395?